| Abstract: | We have identified an endonuclease(s) that preferentially cleaves the internucleosomal linker regions in the aleurone chromatin producing mono- and oligonucleosomes. This enzyme(s) has been designated as a "linker"-specific nuclease(s). This nuclease does not require divalent cations for activity, and therefore it is not the "Ca2+-Mg2+-DNase" found in mammalian cells. The linker-specific nuclease activity is not detectable in the dry aleurone tissue and in the tissue treated with 0.5 mM cordycepin. The endonuclease activity of the aleurone tissue incubated with gibberellic acid is higher than the level of this endonuclease in tissue treated with abscisic acid or water alone. Nuclei isolated from embryos have lower levels of endonuclease activities compared to those from aleurone tissue. Digestion of the nuclei from embryos with micrococcal nuclease revealed the subunit structure of chromatin. In Southern blots of the HindIII digests of DNA from embryos, five DNA bands hybridized to a nick-translated alpha-amylase cDNA clone. In similar autoradiograms with aleurone DNA, particular bands are less visible, notably in the DNA isolated from the tissue treated with gibberellic acid. This is the first report of the presence of a linker-specific nuclease activity in plant cells. |
